1. Field of the Invention
The present invention relates generally to wafer inspection and more particularly to a system and method for automatically moving a wafer within the focus of a scanning electron microscope used in semiconductor wafer inspection.
2. Background of the Invention
Improvements in the semiconductor manufacturing technology have allowed for designing and manufacturing of higher density Very Large Scale Integrated (VLSI) circuits and packing more transistors on a given surface area to form a semiconductor device or chip. Increasing transistor density on a given chip has led to the need for method to provide electrically related, higher resolution wafer inspection. In semiconductor device manufacturing processes, defects may be unintentionally generated during the various stages of semiconductor processing. Thus, it is important to find defects accurately and efficiently as early as possible.
Generally, a process for manufacturing semiconductor devices comprises the operation of forming layers of a variety of material on or in the substrate of each semiconductor device; photo-processing, masking and printing circuit patterns on the semiconductor device; and removing or etching portions of the layers to form the semiconductor device. Such semiconductor devices are manufactured by repeating these and other operations on each device of a semiconductor wafer. Better manufacturing techniques have allowed for micro fabrication, resulting in features that are less than 0.1 xcexcm. Inspections of the wafer are made to check for obtaining defect free devices.
Conventional wafer inspection methods consist of a high magnification and high resolution imaging system, where the photomask is scanned pixel by pixel by a laser diode. Other wafer inspection methods call for the use of optical microscopes in the wafer inspection. Scanning Electron Microscopes (SEM) have been used in some defect detection methods such as critical dimension measurement. With the increasing numbers of transistors packed on a chip, more efficient and more accurate wafer inspection detection method is desired.
Therefore, it is desirable to provide a method and system capable of providing a new means for wafer inspection, better suited for the emerging super higher density semiconductors.
It is an object of the present invention to provide an SEM system and method for positioning a specimen to the focal point of an SEM for inspecting defects in the specimen.
An SEM lens design result in an ideal theoretical focal plane, at which point peak performance of wafer inspection may be achieved. It is therefore yet another object of the present invention to provide an improved SEM apparatus and method for achieving a higher degree of wafer inspection performance by bringing the wafer under inspection into the ideal focal plane, rather than adjusting the focal point of the SEM. In one embodiment, the present Z-stage can move the wafer precisely to the plan within 0.25 micron range of the ideal focal plane.
Briefly, one embodiment of the present invention includes a method of positioning a specimen situated in a scanning electron microscope environment for inspecting defects in a plurality of areas of said specimen, the scanning electron microscope providing a particle beam along an axis perpendicular to the specimen. The method including moving said specimen in directions perpendicular to said particle beam axis to a first of said plurality of areas; sensing and moving the specimen toward a focal plane of the particle beam in a direction along the particle beam axis; suspending moving the specimen when the specimen is positioned within the focal plane proximity and the proximity of said first of said plurality of areas; scanning and inspecting the first of said plurality of areas for defects; and moving said specimen from the first inspection area to a second of said plurality of areas for inspection.
Yet another aspect of the present invention is embodied in a system of positioning a specimen situated in a scanning electron microscope environment for inspecting defects in a plurality of areas of said specimen, the scanning electron microscope providing a particle beam along an axis perpendicular to the specimen. The system including means for moving said specimen in directions perpendicular to said particle beam axis to a first of said plurality of areas; means for sensing and moving the specimen toward a focal plane of the particle beam in a direction along the particle beam axis; means for suspending moving the specimen when the specimen is positioned within the focal plane proximity and the proximity of said first of said plurality of areas; means for scanning and inspecting the first of said plurality of areas for defects; and means for moving said specimen from said first inspection area to a second of said plurality of areas for inspection.
One advantage of the present invention is that it provides an improved SEM focusing method and system used for defect detection in semiconductor wafer inspection systems.
These and other objects and advantages of the present invention will no doubt become apparent to those skill in the art after having read the following detailed description of preferred embodiments which are illustrated in the several figures of the drawing.